Research On Design Principles Of Low-grade Asphalt Mixture Based On Three-level Dispersed System

With the rapid development of economy and thus the rapid increase of traffic, Hightemperature rutting has become the most prominent early disease of asphalt pavement. Inorder to enhance the rutting resistance of asphalt pavement, on the one hand improving theaggregate gradation, and the other hand using of hard asphalt and modified asphalt. In the pasttwo years, the tendency is using of low-grade hard asphalt. While people gradually recognizethe high-temperature performance of low-grade asphalt, the worry of its low temperatureproperties is concerned. After all, low temperature cracking is basically the main problem ofasphalt pavement in the world. In this paper the method of rheology is adopted to study thethree-level dispersed system containing asphalt, asphalt rubber paste and asphalt mortar,aiming at analyzing the influence factors of low grade asphalt mixture performance at lowtemperature, and which are checked by the mixture test. Therefore, the design principles oflow-grade asphalt mixture are obtained.The research results show that with the grade of asphalt is reduced, the asphalt ofhigh-temperature performance is improved and low-temperature performance is reduced atthe same time, ductility index and rheological index of low-temperature performance arealmost have the same sequence, which shows that the operation of ductility index hascredibility, meanwhile suggests that15℃should be used as test conditions of ductility indexafter aging. Further study of rubber paste and mortar show that increasing the ratio ofpowder/oil and lower the grade of asphalt general have the same influence on low temperatureperformance of asphalt at a certain level. In the end, the research of asphalt mixture which candirect impact on the performance of asphalt pavement indicates that under the condition ofalone increasing asphalt content, low-temperature performance is improved, the dynamicstability of rutting is decreasing simultaneously and so is high-temperature performance.Thecondition illustrates that when considering the low-temperature perfomance, high-temperatureperformance should be taken into account. Under the condition of the ra tio of powder/oil isinvariable, adding the amount of asphalt rubber paste in the mixture, the low-temperatureperformance is improved and high-temperature performance has no loss in the meantime.The results consistently show that asphalt grade is the main factor influencing theperformance of asphalt mixture at low temperature, but with the adding of ore and aggregates,the influence of asphalt grade on asphalt mixture at low temperature will significantly weakengradually, high-temperature performance of asphalt mixture depends mainly on the thicknessof asphalt membrane, powder/oil ratio of asphalt mastic and asphalt mixture reflect the change of the thickness of asphalt membrane have consistency; low-temperature performanceis mainly determined by the amount of asphalt, powder/oil ratio of asphalt mastic is themapping of dinas/oil ratio（the proportion of aggregate and asphalt） of asphalt mixture.Improving the low-temperature performance of asphalt mixture but without prejudice to thehigh-temperature performance as a prerequisite, the design principle of low grade asphaltmixture is keeping a high ratio of powder/oil, increasing the dosage of asphalt mastic in themixture, suggesting that in the project of the proportion about low-grade asphalt mixtureshould limit the minimum asphalt content.